One method of cutting a brittle material includes making a mechanical score on a surface of the brittle material. The score can produce a small crack that extends essentially perpendicular to the surface of the material, and may sometimes be referred to as a vent crack or simply vent. Stress applied to the score line, such that a tension stress is produced across the score line (and consequently the vent crack), grows the vent so that it extends across the full thickness of the material, thereby separating the material into several pieces. The stress may be applied, for example, by bending the material, hence a term often applied to the technique is “score and snap”.
The mechanical score and snap method, wherein a score is produced by the mechanical application of a hard scoring wheel or scribe, suffers in that substantial damage is done to the surface, and to some meaningful depth into the brittle material, so that the edges of the separated pieces are weakened by the presence of small cracks or chips produced during the scoring.
To alleviate this damage, laser scoring techniques were developed that used a laser beam to form a score line, after which stress was again applied. According to this technique, a surface of the brittle material was heated by a laser beam. A cooling fluid was then applied to the heated glass, and the accompanying high stress was capable of producing a rupture of the brittle material at the surface thereof and forming a vent crack. Separation occurred after the subsequent application of a bending stress. Variations of the technique include so-called full body separation wherein, instead of first forming a score line, the heating and cooling is sufficient to produce a vent that extends through the full thickness of the brittle material without the application of a subsequent bending stress. While laser scoring has proved to be superior to mechanical scoring, the technique suffers from inconsistencies, largely as a result of the cooling phase.